[(1,2,5,6-η)-Cycloocta-1,5-diene](1-ethyl-4-isobutyl-1,2,4-triazol-5-ylidene)(triphenylphosphane)rhodium(I) tetrafluoridoborate

There are two independent ion pairs in the asymmetric unit with each complex cation exhibiting a distorted square-planar conformation around the rhodium(I) atom.

The title complex, [Rh(C 8 H 12 )(C 8 H 15 N 3 )(C 18 H 15 P)]BF 4 (2), comprises a cationic Rh I complex and a tetrafluoridoborate counter-anion, with molecular structures illustrated in Fig. 1; there are two independent ion pairs in the asymmetric unit.The coordination sphere around the Rh I cation, formed by the bidentate COD, NHC, and triphenylphosphane ligands, results in a distorted square-planar conformation, characterized by C NHC -Rh-P bond angles of 89.6 (2) � for cation A and 89.8 (2) � for cation B. The N-C-N bond angles of the NHC ligand are 102.4(7) and 103.8 (6) � for cations A and B, respectively.Other selected bond lengths in cations A and B are Rh-C NHC = 2.030 (8) and 2.043 (8) A ˚, Rh-P = 2.3211 (18) and 2.3260 (15) A ˚, respectively.Fig. 2 shows a molecular packing diagram of the salt viewed along the a axis, with several close C-H� � �F contacts (likely, non-standard hydrogen-bonding interactions) stabilizing the orientation of the [BF 4 ] À anions with respect to the Rh I complex cations.The non-standard hydrogen-bonding interactions are shown as dotted orange lines in Fig. 2 and are summarized in Table 1.

Figure 3
Overlay of complex A of the salt, shown in red, with previously characterized (Lerch et al., 2024c) neutral complex (1), showing that the Rh-C NHC bond has rotated 180 � in the synthesis of the cationic complex from the neutral precursor.The overlay is constructed with C NHC , Rh, and Cl/P atoms matched between the neutral complex (1) and complex A of the title salt ( 2) with an r.m.s.deviation of 0.029 A ˚between the matched atoms.
anti-configuration with respect to each other when the C NHC , Rh, and P atoms are matched between A and B, as seen in Fig. 4.

Figure 5
Reaction scheme for the synthesis of the title salt (2).

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.

Figure 1
Fig.2shows a molecular packing diagram of the salt viewed along the a axis, with several close C-H� � �F contacts (likely, non-standard hydrogen-bonding interactions) stabilizing the orientation of the [BF 4 ] À anions with respect to the Rh I complex cations.The non-standard hydrogen-bonding interactions are shown as dotted orange lines in Fig.2and are summarized in Table1.An overlay of the neutral precursor complex, chlorido-[(1,2,5,6-�)-cycloocta-1,5-diene](1-ethyl-4-isobutyl-1,2,4-triazol-5-ylidene)rhodium(I) (1)(Lerch et al., 2024c), and cation A of the title salt (2) (Fig.3), shows that in (2) the Rh-C NHC bond, and hence the entire NHC ligand, is rotated by almost 180 � with respect to the remainder of the complex as visualized by the ethyl and isobutyl substituents not overlapping when the C NHC , Rh, and Cl/P atoms are matched with the neutral complex (1).A similar rotation is observed in complex B. The two cations in the asymmetric-unit exhibit different configurations of the ethyl and isobutyl substituents with cation A showing a syn-configuration and cation B showing an

Figure 2
Figure 2Molecular packing diagram of the title salt visualized along the a axis with non-standard hydrogen-bonding interactions shown as dotted orange lines.

Figure 4
Figure 4Overlay of complex A, shown in red, with complex B of the title salt showing the difference in orientation of the ethyl and isobutyl substituents with respect to the NHC ligand.The overlay is constructed with C NHC , Rh, and P atoms matched between the two cations of with an r.m.s.deviation of 0.008 A ˚between the matched atoms.

Table 2
Experimental details.